1. Field of the Invention
The present invention relates to an image sensor device for converting an optical image into an electric signal, and more particularly to a direct-contact type image sensor device and an image sensor unit in which the image sensor device is used.
2. Description of the Related Art
FIGS. 9A and 9B show a conventional direct-contact type image sensor device in which an optical fiber array is used. FIG. 9A shows a front cross-section of the device, while FIG. 9B shows a side cross-section thereof. An image sensor chip 81 is mounted on a substrate 87 having an optical fiber array 83 in such a way that a photosensitive element array 82 is disposed on one end of the optical fiber array 83. Optical image information of a document original 90 disposed so as to be in direct contact with the other end of the optical fiber array 83 is led into the photosensitive element array 82 so as to be converted into an image signal.
However, an image sensor of the above configuration has a problem of poor performance in reading images. The problem is typically caused by the fact that light emitted from light source 85 and light reflected from the document original 90 may have cross-talk among optical fibers constituting the optical fiber array 83, and that there may be redundant optical information due to an unnecessary portion of light emitted from the light source 85 and an unnecessary portion of reflected light.
U.S. Pat. No. 5,065,006 discloses a direct-contact type image sensor in which an optical fiber array is used, as is shown in FIGS. 10 to 12. In the image sensor disclosed in this patent, a black-color film is provided on each of the opposite sides of the transparent substrate so as to reduce the above-mentioned optical crosstalk and flare light. As is shown in FIG. 12, a black-color film 98 is formed on each side of a transparent glass substrate 97 by screen printing, except in a region through which light is transmitted. An optical fiber array 93 is formed by interposing a multitude of optical fibers shown in FIG. 11 between two portions of the transparent glass substrate 97 and heating the optical fibers at a temperature corresponding to the melting point of glass. Then, a black-color film 98 is formed by applying black resin on the transparent glass substrate 97 by screen printing.
However, the above-mentioned prior art has the following problems: In forming the optical fiber array 93 by compressing the multitude of individual optical fibers, as is shown in FIG. 13A, a boundary line between the optical fiber array 93 and the transparent glass substrate 97 does not necessarily constitute a straight line, but may be an irregular curve having some distortion. In order to form a slit for transmitting light to illuminate the document original 90, the black resin must be applied on the transparent glass substrate 97 while keeping at a distance, as seen from above, from the optical fiber array 93. However, it is difficult to form the black-color film 98 by a screen printing method so as to follow the irregular curve of the boundary line. As a result, the black-color film 98 inevitably is formed having a straight line at its boundary line with the slit, as is shown in FIG. 13B. Accordingly, the width of the resultant slit fluctuates depending on the point of measurement. The fluctuation is, at maximum, approximately 200 .mu.m (peak to peak). When the slit is formed with such an accuracy with respect to the width thereof, the amount of light used for reading an image also fluctuates, resulting in fluctuation of .+-.15% or more in the illuminance at a face of the document original 90. Therefore, the image sensor device inevitably has variations in sensitivity.